The Novak Guide to the
Aisin-Warner AX15 Transmission
The Aisin Warner AX15 transmission is a very successful, medium-duty, standard shift, five-speed transmission. It was introduced in the 1988 (mid-year) YJ Wrangler and XJ / MJ Cherokee / Comanche Jeeps, and found in 1988-1999 Jeep XJ, YJ & TJ models. Its only year in the ZJ Grand Cherokee was 1993, and only with the six-cylinder.
The AX15 is found behind the AMC 258 and the Mopar 4.0L (242 ci) I6 engine. The AX15 is also found in Dakota trucks and is closely related to the Toyota R151 as found in the Supra Turbo and Four Runner, though the case rear halves and gear ratios vary. It is also related to or referred to as the AN5, AR5, MA5 in GM and Isuzu applications.
The AX15 was available in Jeeps in both 2wd (typ. XJ / MJ applications) and 4wd versions.
The AX15 is a split-case, top shifting, overdrive transmission with the shifter being located in the rear section of the transmission. The AX15 is fully synchronized in all gears. All gears are helically cut.
Gear ratios for the AX15 are: 3.83, 2.33, 1.44, 1.00, 0.79, for first through fifth, respectively.
The 4wd version of the AX15 transmission case is 16-1/2" long. It features a cast aluminum case with a cast-aluminum mid-plate. The case is generously ribbed and features the shifter in the rear quarter of the assembly. In the vein of newer transmissions, the AX15 uses dowel pins for bellhousing alignment.
The 4wd version of the Jeep AX15 has a 23 spline output shaft for connecting to the transfer case input shaft. This shaft protrudes about 1/2" past the rear face of the transmission.
The AX15 was used with an internal slave/throwout assembly up through the 1993 model year. In 1994, a more conventional slave cylinder and cross-arm were used. The input shaft is a 10 spline x 1-1/8" and its stickout length is 7-1/2".
1988 to 1991 AX15 input shafts have a smaller (~19/32") pilot tip. 1992-1999 AX15's have a larger (~3/4") pilot tip.
The AX15 looks similar to the AX5 and are they are occasionally confused in identification as well as interchange.
|Adapting the AX15 to the Jeep Dana 300|
Transfer Case Compatibility
The Jeep AX15 was factory-married to the Jeep Jeep New Process (aka New Venture) Model 231 transfer case.
It is possible to adapt the AX15 to the Jeep Dana 300 transfer case in passenger side and driver side drop by using Novak kit #153.
Marrying the AX15 to the NP207 transfer case as found in earlier YJ and XJ Jeeps requires that the 207's longer input gear be shortened with a hard saw or lathe to 2.1" of stickout length. This prevents bottoming of the input gear in the spline lead-outs of the AX15's mainshaft.
AMC / Mopar Jeep
As the AX15 was married to the Jeep engines mentioned above, it is OEM compatible with them. It can also be adapted to 1972-1991 AMC I6 & V8 engines following this procedure.
Individuals, hoping to replace their AX5 occasionally assume the AX15 will replace it directly. The bellhousing patterns and spline counts between these similar appearing transmissions are deceivingly close, but not compatible.
|Adapting the AX15 to GM Bellhousings|
The AX15 actually makes a very clean conversion to most GM engines and because it is a stronger transmission, it is well matched for the Chevy V6 and Chevy Small Block V8 and Gen. III+ V8 engines. Details on these conversions can be found here. You may also find the following articles of interest:
The factory manuals call for 75W90 GL-3 gear oil for the AX15 transmission. It is the experience of some that a 50W fluid provides quicker shifts and especially so in colder climates.
The AX15 is one of the good successes for Jeep transmissions. They are generally regarded as the best five-speed transmission ever installed into a Jeep. They are an excellent gearbox, and remain in production by Aisin-Warner as and are available from Novak, new, in their most improved version.